Final answer:
The three main classification domains are Bacteria, Archaea, and Eukarya, with Archaea and Bacteria comprising the prokaryotic organisms, and Eukarya consisting of eukaryotic organisms such as plants, animals, fungi, and protists.
Step-by-step explanation:
The three main classification domains are Bacteria, Archaea, and Eukarya. Organisms within the domain Eukarya have a nucleus and include plants, animals, fungi, and protists. In contrast, the domains Archaea and Bacteria consist of prokaryotic cells, which lack a nuclear membrane.
Archaea are known for their ability to thrive in extreme environments, thus earning them the name extremophiles. The recognition that Archaea were distinct from Bacteria and more closely related to Eukarya was a significant development in our understanding of the tree of life.